Current systems for decelerating a vehicle include wheel braking. Wheel braking is achieved by using friction to convert the kinetic energy of the rotating components of the vehicle to thermal energy which is dissipated to the environment. However, when the driver of the vehicle requires immediate deceleration, the driver typically must first reduce pressure on the accelerator pedal and move the foot to the brake pedal, then depress the brake pedal. This delay can be very significant in determining whether the vehicle is able to stop in time.
Another method of deceleration is via motor braking, where the vehicle decelerates during standard operation by way of the coupling between the motor and the drive wheels. This coupling may or may not include a discrete ratio or continuously-variable transmission. Motor braking may occur from via the internal-combustion engine, through friction and pumping losses, and/or an electric motor/generator in power generation mode.
During such braking which can occur during regular operation, some control systems may inhibit the transmission from shifting to a numerically lower speed ratio. However, this may not provide any substantial reduction in speed, especially if the transmission is already at a numerically lower speed ratio (which is typical when the vehicle is simply cruising at speed). In addition, some control methods can command a shift to a numerically higher speed ratio if a brake input is given from the driver under certain conditions and/or is higher than a predetermined threshold, or if other on-board vehicle systems detect an imminent crash event. However, with such systems, if the vehicle is in motion with an automatic transmission in a numerically lower speed ratio (such as overdrive) and/or an electric motor/generator is not in power generation mode, then the vehicle will initially offer little brake force in the form of motor-braking in between the time when the driver rapidly releases the accelerator and then applies pressure to the brake pedal.
Some control systems can detect that the accelerator pedal is no longer depressed and actuate a brake in response thereto. However, such systems can inaccurately and inefficiently brake the vehicle, and can cause the vehicle to brake even when braking was not intended. Moreover, such systems can cause undue wear to the brake system, and can require significant additional components or costs. In addition, such systems can have other disadvantages. For example, if the friction elements are wet (from rain, snow, etc.) the initial response/capacity may be slower or lower. Moreover, the friction elements may have diminished braking capacity (brake “fade”, boiled brake fluid, etc.) from prior use (such as braking while traveling downhill.) In addition, the friction elements are maintenance items which need periodic replacement; if the parts are near the end of their life they may not have adequate brake response and capacity.
In such instances, the vehicle may not be providing substantial and efficient deceleration at the earliest correct indication of the driver's intent to decelerate the vehicle. The delay and/or other shortcomings associated with other methods and systems can be very significant in adequately and efficiently braking the vehicle. Accordingly, improved methods and systems are desired for providing automated control of vehicle braking.